This invention relates to a pack for food products comprising a metal container and a removable cover adapted to the container.
Food products of the frozen prepared dishes type are generally presented in metal containers, for example of aluminium. The containers are closed by a lid, for example of aluminium foil or cardboard, and accommodated in a cardboard pack. To cook or reheat the product, the lid is removed and the container is placed in an oven. Other culinary products, intended for example for the easy preparation of flans, pies or tarts based on baked custard, salted or sweetened, may be formed by a precooked pastry base already in place in a metal container and by a bag containing ingredients making up the filling, for example in dehydrated form. To prepare the dish, the housewife merely has to add the necessary quantity of liquid, for example milk and egg, preferably mixed beforehand, to the dehydrated ingredients and then to cook the product in the oven. The metal containers are perfectly suitable for conventional convection or infrared ovens, but have serious disadvantages for microwave ovens.
The rapid progress in the sale of domestic microwave ovens and the development of industrial catering have brought changes in the conditions under which prepared dishes are made, creating both advantages and problems. The advantages are obvious and are associated with the rapid heating by microwaves which makes the frozen products, for example, even more convenient to use, however, there are several problems in that:
The traditional metal container is opaque to microwave radiation and is unsuitable for microwave ovens because arcing can occur in the oven cavity, which can damage the walls of the oven, or radiation can be reflected towards the magnetron which can thus be damaged if inadequately protected, as for example in ovens of relatively old design. PA0 The cooking of certain products is very uneven because the metals in the form of a conductive foil are not transparent to microwaves and heating takes place downwards. Accordingly, the upper layer is preferentially exposed to the effect of the microwaves, which have only a weak penetrating power, with excessive generation of heat and evaporation of water. In the case of deep-frozen products in particular, this results in uneven cooking with the bottom layer cold, and even still frozen, while the upper layer is dry, or even burnt. In the specific case of the preparation of a baked custard, the use of a microwave oven leads to a movement of the product, preventing correct coagulation of the baked custard. Instead of being smooth, the texture of the baked custard is more like that of scrambled eggs. PA0 Cooking is not only uneven, it is also slow.
Certain development work in the packaging industry in association with microwave cooking has dealt with the problems involved in the selective cooking of multicomponent meals in which the individual components of the meal require different quantities of microwave energy.
For example, U.S. Pat. No. 3,865,301 describes a container formed with apertures which is adapted to several ingredients of a food product of the sandwich type which have to be heated or cooked to different degrees. The container in question is opaque to microwave radiation except for the apertures which are transparent to microwaves.
U.S. Pat. No. 4,081,646 shows a container consisting of a material which is transparent to microwaves and comprising several compartments, a cover made of a material transparent to microwaves and adapted to the container and an apertured box having walls opaque to microwaves and apertures in predetermined positions into which the container and the cover are inserted so that the quantity of radiation received by each of the individual components of the meal may thus be controlled.
Other work has concentrated on the production of containers which are designed to allow both uniform regeneration or cooking and protection of the materials involved, for example cardboard or plastics, in domestic or microwave ovens equipped with infrared grills. For example, U.S. Pat. No. 4,351,997 describes a container of a material transparent to microwave radiation of which the inner surface of the side wall or the corners and the upper part thereof forming the horizontal edge are covered with a metallic material which is opaque to microwaves. A container such as this is difficult to manufacture.
Finally, U.S. Pat. No. 4,439,656 relates to a utensil of a material transparent to microwaves in which a metal container is placed and which, after filling with water, enables the microwave oven to be protected and a food to be uniformly cooked. The consumer does not always possess such a utensil which is sold separately from the food. In addition, a utensil of the type in question cannot be adapted to all the various container shapes although it ought to accommodate several.